The overall goal of our studies is to develop an effective vaccine to prevent rabbit pasteurellosis. This proposal focuses on the development of outer membrane protein vaccines. The P. multocida outer membrane proteins which are immunogenic, exposed on cell surfaces, and accessible to protective antibodies in whole intact cells are potential vaccine candidates. Therefore, these cell surface-exposed proteins will be identified, purified, and tested in rabbits for their ability to elicit protective antibodies. The cell surface-exposed P. multocida outer membrane proteins will be identified by the whole cell immunoprecipitation using rabbits immune serum against KSCN extracts of 3:A or 12:A P. multocida. To prove that the specific outer membrane protein is protective it is essential to purify this particular outer membrane protein and test its ability to elicit protective antibodies in rabbits. Monoclonal antibodies directs to these cell surface-exposed P. multocida outer membrane proteins will be used for purification of the desired P. multocida outer membrane proteins by the affinity chromatography, determination of the protective ability of the murine monoclonal antibodies in mice and analysis of the antigenic composition of the P. multocida rabbits isolates to identify the common or cross-reactive antigenic determinants among these P. multocida isolates. The purified outer membrane protein will be tested for its ability to stimulate protective antibodies in rabbits by passive transfer of the immune rabbit serum to normal rabbits (pasteurella free; free of P. multocida antibodies) and challenge with the virulent homologous P. multocida organisms. Similarly, the P. multocida outer membrane proteins(s) which are common to or cross-reactive with most strains of P. multocida rabbit isolates will be identified, purified, and tested in rabbits.